1. Field of the Invention
This invention relates generally to the field of machine tool equipment, and more particularly to a face grooving tool holder adaptable for holding a cutting insert for cutting circular face grooves having widely differing diameters in the end face of a workpiece without interchanging tool parts.
2. Background Art
A well known machine tool operation is known as "face grooving." Face grooving is an operation for cutting a circular groove in the end face of a metal workpiece. In such an operation, a tool holder apparatus, bearing a small cutting element called an "insert," is mounted on a machine tool and is utilized in a manner described in more detail below.
A workpiece defining a generally longitudinal axis is clamped into a rotatable chuck of the machine tool. The machine tool includes power drive apparatus for rotating the chuck such that the workpiece rotates substantially about its longitudinal axis.
The tool holder, carrying the cutting insert, is supported by the machine tool so that the cutting insert extends generally toward the end face of the workpiece mounted in the chuck. The machine tool includes apparatus for translating the tool holder, and thus the cutting insert, transversely of the axis of rotation of the chuck and for moving the tool holder axially of the chuck, i.e., toward and away from the end face of the workpiece.
In a face grooving operation, the workpiece is mounted in the chuck and the chuck is power driven to rotate the workpiece. The tool holder is translated, relative to the rotational axis, to a location at which, when advanced against the end face of the workpiece, the cutting insert will scribe, or cut, a groove of a desired diameter in the workpiece end face. When the cutting insert is positioned at the desired displacement from the rotational axis, the cutting insert is advanced against the end face of the workpiece, and a groove is cut in the workpiece end face. The diameter of the end face groove is dependent upon the degree of displacement of the cutting insert from the axis of rotation.
Since the present invention relates specifically to a tool holder assembly, a prior art face grooving tool holder is now described, with particular reference to FIG. 1a. The tool holder, generally designated at 10, includes three main parts: a main body 12, a support blade 14 and a clamping arm 16.
The main body 12 is a heavy piece of steel adapted to firmly support the remaining portions of the tool holder. The main body is configured to define flats, such as 18, which facilitate its firm mounting in the machine tool. The main body portion also defines a recessed portion 20, adapted for accommodating the blade 14 and the clamping arm 16.
The blade is demountably attachable to the main body portion 12 by means of known fasteners, such as screws. Likewise, the clamping arm is removably mountable on the main body portion in a location such that the clamping arm bears down on the upper surface 22 of the blade 14.
In use, a cutting insert 24 is placed atop a recess in the upper surface 22 of the blade. The clamping arm is then applied and fixed in place such that the lower edge 28 of the clamping arm, in cooperation with the upper edge of the blade, holds the cutting insert 24 firmly in place. The cutting insert can easily be removed and replaced by simply loosening the clamping arm, replacing the cutting insert and retightening the clamping arm in its fixed position.
A prior art tool holder is illustrated and described in U.S Pat. No. 3,611,525, issued Oct. 12, 1971 to Cochran. A cutting insert of known design is illustrated and described in U.S. Pat. No. 3,802,042, issued Apr. 9, 1974 to Novkov. Both of these issued United States patents are hereby expressly incorporated by reference.
It can be seen in FIG. 1a that the support blade 14 exhibits a curvature. The curvature is desirable because, during a face grooving operation, the blade, in the course of firmly supporting the cutting insert, actually protrudes with the cutting insert into the groove which is being cut. Since the groove is circular in configuration, it is desirable that the blade have a radius of curvature similar to that of the face groove being cut. If the blade were not so curved, portions of the blade would impinge, during cutting, against the inside or outside walls of the face groove.
It has been proposed, as an alternative to curving the blade, to simply use a blade with a shorter dimension from its top surface 22 to its trailing edge 28. This has not been entirely successful, however, because such a configuration results in a blade having mechanical strength characteristics inferior to that of curved blades such as are described above.
Another proposed alternative is to taper the trailing edge 28 of the blade, in order to afford more clearance between the trailing edge of the blade and the inside and outside walls of the face groove being cut, to allow use with a range of groove diameters. This increases the cost of machining the blades, and also reduces the blade strength.
Due to the fact that the curvature of the curved blade is fixed and cannot be changed, and only a limited clearance is available between the groove walls and the blade width, a particular blade can cut face grooves having diameters which can vary only slightly. For example, a typical single curved blade for cutting small diameter grooves is adaptable for cutting face grooves having diameters of only between 2 inches and 21/4 inches and for example, a single blade for cutting large diameter grooves can cut grooves ranging between 12 and 18 inches in diameter.
Clearly, a problem arises when one wishes to cut face grooves of widely differing diameters. In the past, it has been proposed to facilitate this by employing a set of support blades having different curvatures in order to accommodate the cutting of grooves of widely differing diameters. Two blades 14a, 14b of a set of such blades having different curvatures are illustrated in FIG. 1b. The blades have top surfaces 22a, 22b and trailing edges 28a, 28b. In order to afford the versatility of cutting face grooves of different diameters, e.g., grooves between 2.5 inches and 18 inches in diameter, a set of several different blades having differing curvatures had to be provided, for example, four to six blades to cover the above-mentioned range. The necessity of providing these additional support blades increased considerably the cost of the tooling apparatus and inventory required.
Additionally, the necessity for changing cutting blades when changing cutting diameters increased labor costs and down-time in the face grooving operation.
It is an object of the present invention to provide a face grooving tool holder which is adaptable for cutting face grooves of widely varying diameter without the necessity for providing multiple support blades.